linux-kernel - Re: [PATCH 4/5] mm, hmm: replace hmm_devmem_pages_create() with devm_memremap

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Date:   Tue, 22 May 2018 11:13:41 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Dan Williams <dan.j.williams@...el.com>, akpm@...ux-foundation.org
Cc:     Christoph Hellwig <hch@....de>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] mm, hmm: replace hmm_devmem_pages_create() with
 devm_memremap_pages()



On 21/05/18 04:35 PM, Dan Williams wrote:
> +	/*
> +	 * For device private memory we call add_pages() as we only need to
> +	 * allocate and initialize struct page for the device memory. More-
> +	 * over the device memory is un-accessible thus we do not want to
> +	 * create a linear mapping for the memory like arch_add_memory()
> +	 * would do.
> +	 *
> +	 * For all other device memory types, which are accessible by
> +	 * the CPU, we do want the linear mapping and thus use
> +	 * arch_add_memory().
> +	 */
> +	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> +		error = add_pages(nid, align_start >> PAGE_SHIFT,
> +				align_size >> PAGE_SHIFT, NULL, false);
> +	} else {
> +		struct zone *zone;
> +
> +		error = arch_add_memory(nid, align_start, align_size, altmap,
> +				false);
> +		zone = &NODE_DATA(nid)->node_zones[ZONE_DEVICE];
> +		if (!error)
> +			move_pfn_range_to_zone(zone, align_start >> PAGE_SHIFT,
>  					align_size >> PAGE_SHIFT, altmap);
> +	}

Maybe I missed it in the patch but, don't we need the same thing in
devm_memremap_pages_release() such that it calls the correct remove
function? Similar to the replaced hmm code:

> -	mem_hotplug_begin();
> -	if (resource->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY)
> -		__remove_pages(zone, start_pfn, npages, NULL);
> -	else
> -		arch_remove_memory(start_pfn << PAGE_SHIFT,
> -				   npages << PAGE_SHIFT, NULL);
> -	mem_hotplug_done();
> -
> -	hmm_devmem_radix_release(resource);

Perhaps it should be a separate patch too as it would be easier to see
outside the big removal of HMM code.

Logan